Strange GTI fuel pump noise......

accumulator isnt easy to clean out, unless you mean the plastic fuel reservoir before the main pump? if so yeah give it a good clean out but i would use petrol. plenty will go everywhere when you disconnect fuel system so put a container under it and dont let it go to waste. its bloody great and cleaning stuff

Well the cars been sat for a while - i gave up, it now won't start at all - i have fuel pressure to the 5th injector but it doesn't seem to work, when measuring voltage on both the 5th injector and the TTS it flicks to 9v the first time you try to start it then no more than .48v thereafter - do these parts have a specific relay?

no relay, it gets power direct from the starter motor, and earths via the 5th injector thermoswitch

That earth looks bloody awful - might be part of the problem - will get that changed.